The present invention relates to a hydraulic circuit, such as a hydraulic circuit for a vehicle.
Known vehicle hydraulic systems have both low and high pressure devices or circuits. For example, a known production tractor includes an infinitely variable transmission (IVT) which includes an electro-hydraulic hydrostatic drive unit and a hydro-mechanical transmission. The electro-hydraulic hydrostatic drive unit requires a supply of high pressure hydraulic fluid for operation of a yoke which controls a variable displacement unit, whereas the hydro-mechanical transmission requires only lower supply pressure to operate its transmission control clutches.
In a vehicle hydraulic system, overall system flow requirements are typically dictated by pump sizing at low engine speed, which then results in higher flows and more power loss at higher engine speeds. In this known production system a single high pressure gear pump supplies hydraulic fluid to both these high and low pressure hydraulic components. This single pump must be sized so that it can supply sufficient amounts of hydraulic fluid at low idle engine speeds. However, as a result, at high engine speeds it will supply more hydraulic fluid than is required, producing surplus hydraulic fluid flow and wasting engine power.
Conventional vehicle hydraulic systems have parasitic losses which reduce available hydraulic power. Certain systems use a variable displacement pump to reduce flow as engine speed increases. Other systems use positive displacement gear pumps. But, as engine speed increases, so does hydraulic flow and ultimately, power losses.